In the common use of a polyurethane polishing pad, the pad surface which contacts the part to be polished is typically conditioned before and during polishing. One problem encountered during the use of polyurethane foam polishing pads is the continuous need to recondition the pact. Conditioning in most polishing applications involves moving a conditioning tool across the pad contact surface which creates a nap of sheared polyurethane, flattens out pad topography, and cleans out accumulated slurry and swarf from pores. A conditioning tool can comprise a metal puck that is impregnated on one side with diamond powder or another similarly hard abrasive material. In the normal course of polishing, a polishing pad will experience a decline in performance (i.e., Stock removal, part flatness, part defects, and/or surface roughness) that is related to the flattening of the polyurethane nap, changes in the pad topography, and dogging of pores with slurry and swarf.
Polishing pads are useful in many applications. Two such applications are polishing glass and polishing wafers. Regardless of the application, a polishing pad is moved relative to the object (e.g., glass, Si wafer, Sapphire wafer, etc.) being polished. This relative movement may be created by rotating the polishing pad, by rotating the object being polished, or a combination of such movements. Other linear or any useful relative motion may be used between the polishing pad and the object being polished. In some embodiments, a force may be applied to press the polishing pad in contact with the wafer.
The polishing may be performed to varying degrees such as to remove larger imperfections, to achieve a mirror finish and/or final flatness, etc.
Conventionally, the process of polishing silicon semiconductor substrate wafers to improve flatness is accomplished by a mechanochemical process in which one or more polishing pads, typically made of urethane, is used with an alkaline polishing solution (slurry), commonly comprising fine abrasive particles such as silica or cerium. The silicon wafer is supported between a platen covered with a polishing pad and a carrier to which the wafer is attached, or, in the case of double-sided polishing, the wafer is held between two platens, each covered with a polishing pad. The pads are typically about 1 mm thick and pressure is applied to the wafer surface. The wafer is mechanochemically polished by relative movement between the platen and the wafer.
During polishing, pressure is applied to the wafer surfaces by pressing the pad and the wafer together in a polishing tool, whereby a uniform pressure is generated over the entire surface owing to the compressive deformation of pads. Polishing tools often have dynamic heads which can be rotated at different rates and at varying axes of rotation. This removes material and evens out any irregular topography, making the wafer flat or planar.
Unfortunately, typical prior art polishing pads tend to need to be conditioned and therefore replaced frequently because conditioning removes a portion of the pad thickness. For example, such polishing pads may need to be replaced every 5-10 days. It is desirable to have a polishing pad that can maintain its optimal polishing performance longer before conditioning is necessary, thereby giving the polishing pad a longer polishing life. In this manner, more polishing can be performed and thus more product can be made in a set period of time. In this regard, it is desirable to have a polishing pad that is self conditioning.